Vehicles having an internal combustion engine can operate in a variety of modes. As one example, an engine may operate in a spark ignition (SI) mode, wherein a charge of a mixture of air and fuel is ignited by a spark performed by a sparking device within a combustion chamber. As another example, an engine may operate in a compression ignition mode, wherein a mixture of air and fuel are compressed within a combustion chamber by a piston, causing ignition of the charge without necessarily requiring the addition of a spark from a sparking device.
One type of compression ignition known as homogeneous charge compression ignition (HCCI) utilizes compression of a substantially homogeneous mixture of air and fuel to achieve controlled auto-ignition (CAI). In HCCI engines, ignition occurs virtually simultaneously throughout a combustion chamber as a result of compression instead of spark ignition, making the combustion process challenging to control. HCCI engines are similar to gasoline engines in having a homogeneous charge, but are similar to diesel engines in having compression ignition. HCCI engines may be used to combine gasoline engine low emissions with diesel engine efficiency.
HCCI combustion engines typically change operation conditions more slowly then other combustion processes. The engine hardware used to control initial cylinder conditions such as internal residuals, intake air temperatures, and the combustion process stability window, limits dynamic response.
In one approach, as described in U.S. Pat. No. 6,725,825, issued to Kurtz, et al., an engine combustion mode may be controlled to improve dynamic response. In particular, Kurtz discusses providing a net torque equal to a driver demanded torque by transitioning a portion of the cylinders from a first to a second combustion mode, such as from an HCCI combustion mode to a SI combustion mode.
However, the inventors herein have recognized disadvantages with this approach. Specifically, transition of a cylinder between combustion modes can increase combustion control challenges, reduce efficiency benefits from combustion ignition cylinders, and increase emissions, increase noise, vibration and harshness (NVH), and provide a less smooth torque delivery.
In a first approach, as described herein, the above issues may be addressed by controlling an internal combustion engine having a plurality of cylinders using electronic valve actuation by operating a first portion of the cylinders in an HCCI combustion mode, operating a second portion of the cylinders in a non-HCCI combustion mode, and adjusting the valve timing of the second portion of cylinders to dynamically load level the engine in response to a transient torque demand.
In a second approach, also described herein, the above issues may be addressed by controlling an internal combustion engine having a plurality of cylinders by operating a first portion of the cylinders in an HCCI combustion mode, operating a second portion of the cylinders in a non-HCCI combustion mode, and adjusting the torque provided by the second portion of cylinders more than adjustment of torque provided by the first portion of cylinders to respond to a transient torque demand. Thus, while torque is adjusted in both cylinder portions, a greater adjustment is provided by the non-HCCI combustion cylinders to enable improved control of the HCCI portion.
In another approach, also described herein, the above issues may be addressed by a system for controlling a multiple cylinder internal combustion engine that includes a first group of cylinders to operate in a homogeneous charge compression ignition mode, a second group of cylinders to operate in a spark ignition mode, and an engine controller operably coupled to the first and second groups of cylinders, said controller to adjust the valve timing of the second group of cylinders to dynamically load level the engine in response to a transient torque demand.